US2202731A - Automatic temperature control - Google Patents

Description

H. R. CRAGO AUTOMATIC TEMPERATURE CONTROL Filed June 16, 1936 May 28, 1940.

Patented May 28, 1940 UNITED STATES AUTOMATIC TEMPERATURE CONTROL Harry E. Crago, Caldwell, N. J., assignor to General Electric Company, a corporation of New York Application June 16, 1936, Serial No. 85,524

12 Claims.

My invention relates to a new and improved automatic condition changing control system and more particularly to a control system of the type in which the condition responsive means of the system are cooperatively associated with periodic time controlled means operating independently of day time or night time.

One of the objects of my invention is to provide a time controlled means for periodically rendering a condition responsive means effective for selectively initiating or terminating operation of a condition changing means only at recurring short periods independent of day time or night time.

A primary object of my invention is to provide an improved control arrangement in which a single condition responsive means is adapted to select for operation the proper condition changing means Whenever the condition is without predetermined limits and time controlled means of the above character cooperatively associated therewith is adapted to terminate operation of the selected condition changing means only after the condition is returned within said limits.

More specifically, it is an object of my invention to provide a control system for condition changing apparatus, such as heating and cooling or humidifying and dehumidifying means, whereby a single condition responsive means may select and initiate operation of the proper means to maintain the condition within desired limits and time controlled means thereafter may insure operation of the selected means for'at least one of a plurality of recurring short periods independent of day time or night time.

It is a further object of my invention to provide the usual means for heating and cooling and means for humidifying and dehumidifying the air with a new and improved control consisting of thermal responsive and time controlled means of the above character for selectively controlling the heating and cooling means and relative humidity responsive and time controlled means of the above character for controlling the humidifying and dehumidifying means.`

It is a further object of my invention to provide an arrangement in which humidication or dehumidiiication may be carried on simultaneously with heating. When the cooling means is in operation humidification may be obtained simultaneously therewith but since the cooling means is also, in accordance with usual practice, the dehumidifying means, dehumidication and cooling will result simultaneously simply from operation of the cooling means.

Another object of my invention is to provide a control in which each condition responsive means requires but a single time controlled means to carry out the desired functions.

A further object of my invention is so to correlate the condition responsive means, time controlled means and the means controlling operation of the condition changing means that the time controlled means periodically renders effective the thermal responsive meansv and the 10 relative humidity responsive means to exert their selecting function and thereafter maintains the selected apparatus operative until a predetermined time after the thermal responsive means move out of its selective position. In this manner I provide a cycling control in which the condition responsive means periodically feels the conditions obtaining within the space being conditioned only at recurring short periods independent of day time or night time. 20

A more specific object of my invention is to provide a novel control in which the pairs of oppositely acting condition changing means are controlled by relays interlocked in such manner that the same thermal responsive and time controlled means may provide cycling control of both of said condition changing means.

These and other objects of my invention will become apparent from the ensuing description taken in conjunction with the accompanying 30 drawing in which is set forth for the purpose of illustration the details of the arrangement.

The single figure of the drawing shows dia-v grammatically air conditioning apparatus designed for year around operation and illustrates 35 schematically a control system therefor embodying the principles and features of the invention.

Referring to the single figure of the drawing, reference numeral I0 designates a space such as a room, building or the like to which conditioned medium such as air is to' be supplied. The air is supplied to the space by an air conditioner Il preferably located without said space and provided with the usual recirculated air duct I2, fresh air duct I3, and a discharge duct I4 leadingto the space. 'I'he proportions of recirculated and fresh air may be controlled by dampers I5 and I6 in the recirculated and fresh air ducts respectively, controlled either manually or automatically in response to indoor or outdoor temperature variations as desired (control not shown). The conditioner is provided also with a fan I 8 positioned in thek discharge duct and driven by suitable motive means such as an electric motor I9 that is adapted to be continuously energized whenever the air conditioning system is placed into operation, as will appear more fully hereinafter.

The air drawn through the conditioner by the fan may be suitably conditioned by heating, coollng and humidifying means forming part of the conditioner and the arrangement is such that either the heating or cooling means may be selec- ,tively energized by thermal responsive means within the space l0 and the humidifying means and the cooling means may be selectively energized by humidity responsive means within the same space. The cooling means is used not only to cool the air but also to dehumidify it when the humidity within the space is above predetermined limits.

The cooling means consists of the usual mechanical refrigerating apparatus of which the evaporator 2li is connected by a refrigerant line 2l to the suction side of a compressor 22. The high pressure side of the compressor is connected by a conduit 23 to a condenser 2d illustrated as being of the air cooled type but which may be cooled in any desirable manner. IThe condenser is connected to a liquid receiver 25 leading through conduit 26 to a thermostatically controlled expansion valve il controlling the flow of refrigerant to the evaporator. The compressor is driven by a suitable prime mover such as an electric motor 29 under the control of both the thermal responsive means and the humidity responsive means within the space ill.

The heating means of the conditioner is diagrammatically illustrated as a coil dil adapted to be supplied with a suitable heating medium such as steam or hot water through a pair of conduits 3l connected to a suitable source. The now of heating medium to the heating coil within the conditioner is controlled by a motor operated valve 32 in the inlet conduit. The motor 33S controlling the operationA of the valve is of a well known type adapted to rotate 180 to operate the valve 32 to its closed or open position each time that it is energized under the control of the thermal responsive means within the space. It should be obvious to those skilled in the art that the source of heating medium may be of any of the well known types that are available and that, instead of controlling the position oi a valve, I may equally well control the energization of means controlling the position of a damper or control the energization of a burner motor associated with an oil furnace.

The humidifier 35 of the conditioner is of a well-known wire screen construction provided with a water inlet pipe it, the supply of water through which is controlled by valve ill having a spring biased operating arm 3@ adapted to be moved from a closed to open position by any suitable operating means such as the electrical solenoid 39 illustrated in the figure.

My invention is not directed to the particular means described above for performing any of the condition changing functions but it is directed to the control to be described hereinafter.

Briefly, the control consists of thermal and humidity responsive y@ .ic-ivices adapted selectively to engage a pair ci cont ets associated with each 'to initiate operation of er 'the heating or coolmeans and the mimi ying or dehnmidiiying means, respectively. Time controlled means are provided ier each of condition responn sive means fior periodioally rendering them ef- :ective to energize electrical means controlling the operation oi the various condition changing asomar means. Upon energization, the electrical means are adapted to be locked in their energized positions by holding circuits comprising other synchronized time controlled means. The synchronized time controlled means are so arranged that the energizing circuit is maintained for only a brief period while the holding circuit is maintained closed during that period of each cycle that the energizing circuit is opened. In this manner, the condition responsive means is used only periodically to feel the condition obtaining within the space. lf the condition is without predetermined limits the apparatus selected for operation by the condition responsive means will be maintained in operation until normal conditions again obtain within the space.

According to my invention I provide a pair of condition responsive means 4l and 42 responsive to temperature and humidity changes, respectively, having associated therewith time controlled means 43 consisting ofthe usual electrical clock motor 44 and a series of cams 45 to 48, inclusive. The clock motor is adapted to be energized continuously through a source of supply 49 whenever a manually operated switch 5d is moved to its closed position and the control itself is supplied with low voltage energy through a transformer 5l having its primary winding connected to the supply conductors 49 through conductors 52. The secondary winding of the transformer is divided preferably, but notJ necessarily, into two portions 53 and 54 adapted to supply energy to the thermal and humidity responsive controls through conductors 55 and 56 and a midpoint conductor 5i. The latter is connected by a conductor 58 to a plurality of cam follower arms 5d to 62, inclusive, associated with each of the cams 45 to 4t, inclusive. Cams i5 to d6, similarly constructed, constitute time controlled means adapted intermittently to render the condition responsive means eiective to energize the various electrical control means controlling the operation of the various condition changing means. Cams 4l and 48, likewise similarly constructed, are adapted, on the other hand, to periodically energize the holding circuits for the electrical control means, as will appear more fully hereinafter. lt may be noted that the synchronized pairs of cams 46, 4l] and 45, 43 are of somewhat different construction the cams 45 and 46 being adapted to close their normally open energizing circuits for brief intervals overlapping the interval that the cams 4l and 48 momentarily break their associated normally closed enengization maintaining circuits.

Conductors t3 and B4 connect contacts associated with cam follower arms 59 and til to the humidity responsive and thermal responsive means 42 and 4l, respectively. The thermal responsive means 4i consists of a thermal responsive element [156, illustrated as a bimetallic element, having associated therewith a pair of ad.,- justably mounted contacts 8l and The former, engageable by element when the temperature decreases below a predetermined value, is connected by a conductor electrical means, such as a re y lil, controlling the s. .Adina engagea by the ther when the tei oeratnre eration ci the cooling' means. actor ing from portion till voi the secondary winding of the transformer is connected to a conductor 13 connecting the relays 10 and 12.

The relays 10 and 12 have associated therewith armatures 14 and 15, respectively, and each armature has associated therewith a pair of switches 16, 11 and 18, 19, respectively. Switches 16 and 18 form interlocks controlling holding circuits for the respective relays and switches 11 and 19 control the heating and cooling apparatus, respectively. The holding circuit for relay 10 extends from conductor 69 through a conductor 8|, a pair of normally open contacts associated with interlock 16, conductor 82, interlock 18 normally in engagement with a pair of contacts and a conductor 83 leading to a contact 84 associated with cams 41. Thevholding circuit for relay 12 extends from conductor 1| through a conductor 85, a pair of normally open contacts associated with interlock 18 and thence through conductor 83 through the above mentioned contact 84.

The valve motor controlling the supply of heating medium is supplied with energy from the supply conductors 49 through a pair of conductors 86 from one of which conductors 81 and 88 to each of a pair of contacts associated with the switch 11 of the heating control. The normally closed contact of switch 11 is connected by a conductor 89 to a limit contact 90 associated with valve motor 33 and the normally open contact is likewise connected by a conductor .9| to a second limit contact 92, The limit contacts have associated therewith a pair of motor operated limit switches 93 and 94 indicated inthe positions they assume with the'valve fully closed. When the valve is in its opposite position, i. e. fully open, the limit switch 94 is disengaged from its associated contact 92 and limit switch 93 engages its associated contact 90. The limit switches are connected to one terminal of the operating winding of the motor by a conductor 95 and the other terminal of the motor winding is connected to conductors 96, 91, and 98 leading to one of the supply conductors 86.

The cooling means is energized through an interlock on the fan control relay preventing the operation of the former unless the fan motor i9 is energized. Conductors 98 and 99 connect the fan control relay |00 directly tothe source of power through branch supply conductors 86 whenever switch 50 is closed. The energization of relay |00 effects upward movement of its associated armature thereby energizing the fan motor I9 through a pair'of conductors |0| and a pair of switches |02. The normally open fan control relay interlock |03 thereby connects one of the supply'conductors to a conductor |04 leading to one of a pair of conductors |05 and |06 adapted to be connected by the switch 19 whenever the relay 12 is energized. Conductor |06 is connected by alconductor |01 to a relay |08 controlling the operation of the compressor motor 29 through a pair of switches |09 adapted to connect the compressor motor to branch supply conductors 98 and 99 whenever the relay is energized.

The control circuits through which the humidication and dehumidiiication may be obtained through operation of the humidity responsive means will now be described in detail. The humidity responsive means 42 consists of an element ||2 moved in response to relative humidity conditions within the space |0. Associated there with is a pair of contacts |13 and H4, the former of which is connected through conductor ||5 to a cooling (or dehumidifying) control relay ||6 having associated therewith anarmature ||1 and a pair of switches ||8 and 9. 'The contact |98 is connected in similar manner by a conductor |20 to a humidifying control relay |2| having associated therewith an armature |22 and a pair of switches |23 and |24. Switches ||8 and |23 are interlocks corresponding to interlocks 16 and 18 of the previously described relay mechanisms and constitute the means for locking the relays whenever the latter are energized. The holding circuit for relay ||6 extends from conductor H5 through a conductor |25, the normally open contants associated with interlock M8 and a conductor |26 leading to a contact |21 associated with cam 88. The holding circuit for relay |2| extends from conductor |20 through conductor |28, the normally open contacts associated with interlock |23, conductor |29, the normally closed contacts associated with interlock ||8 and conductor |26 leading to the aforementioned contact |21. Switch i i9 associated with the cooling control relay ||6 is connected by a pair of conductors |3| and |32 to the conductors |05 and |06 whereby switches 19 and H9 are connected in parallelin such manner that closure by either of their respective contacts will energize the relay |88 controlling operation of the compressor motor. Switch |24 controls the energization of the humidifying means and one of the normally open contacts associated therewith is connected to conductor |05 while the other is connected by a conductor |33 to the solenoid 39 controlling valve The solenoid 39 has its other terminal connected to previously mentioned conductor 91 through a conductor |34.

To initiate operation of the system switch 50 is operated manually to its closed position thereby connecting the supply conductors 89 and the various branch supply conductors 52-86, 98-99 to the source of supply. Upon closure of said switch, relay |00 controlling the operation of the fanmotor is energized through an obvious circuit and its associated switches |02 connect the fan motor to the branch supply conductors 86 through conductors |0I. Interlock |03 associated with the relay also connects conductor 8l to the conductor |04 thereby enabling the cooling apparatus to be operated under the control of the condition responsive means.

The operation of the system as it functions in response to variations in temperature within the zone i0 will rst be given. Upon closure of switch 50 the time controlled means 44 is energized and the cams associated therewith are rotated at a constant speed, preferably one revolution per minute. With the thermal responsive means in a position intermediate its associated contacts none of the relays will be energized.

Assuming rst that the temperature decreases below a predetermined value, then thermal responsive element 66 will engage its associated contact 61, thereby energizing heat control relay 1|) the first time that cam 46 which periodically renders the thermal responsive element 66 effective to initiate heating operation only at recurring short periods closes the circuit connecting conductors 58 and 64. The energizing circuit for the relay is as follows: from the midpoint of the secondary winding of the transformer through conductor 51, conductor 58, cam follower arm 60 in -engagement with its associated Contact, conductor 64, thermal responsive element 66 in engagement with contact 61, conductor 69, the relay winding 10 and conductor 56 back to one terminal of the transformer winding 54.

Energlzation of relay lil results in the establishment of a holding circuit therefor and the opening of the valve 32 admitting heating medium to the heating coil. 3u.

The holding circuit for the relay is established through cam 4l which periodically renders the thermal responsive element effective to terminate heating operation only at recurring short periods and closes its contacts sometime prior to theopening of contacts associated with cam 46. The holding circuit is as follows: from the midpoint of the secondary winding of the transformer through conductor El, conductor all, cam follower arm ti in engagement with contact 8l, conductor titl, interlock l@ in its normally closed position, conductor t2, interlock it in engagement with its associated normally open contacts, conductor di to the relay winding and thence through conductor 5@ to the other terminal of the transformer secondary winding 5d.

The energizing circuit for the valve operating motor 33 extends from one of the pair of branch supply conductors t@ through conductors tl .and td, switch 'lll in engagement with its associated normally open contacts, conductor 9i, limit switch @il in engagement with contact 9??, conductor to the motor winding and from thence through conductors Qt, Elli, and @il to the other of the pair of branch supply conductors d6. Motor is thereby energized to open valve 32 upon rotation of 180 and moves limit switch @El out of engagement with Contact 92 and limit switch into engagement with contact 9d, there' by conditioning the motor circuit for subsequent energizatlon to operate the valve to its closed v position when switch lll moves into engagement with its lowermost contacts,

Heating medium will he supplied to the heating coil t@ until the thermal responsive element lili moves out of engagement with contact till and the above described holding circuit is opened by operation of cam ll. llt will be obvious from the ahove description that as long ras the thermal responsive element remains in engagement with contact Gli each time that the holding circuit is breiten by cam lll the relay l@ is maintained energized through the initial energizing circuit and each time that the energizing circuit is lorollren by cam Il@ the holding circuit maintains it energized. lin this way the thermal responsive element @El is periodically rendered effective for selectively initiating or terminating the heating operation only at recurring short periods. However, upon disengagement of the thermal responsive element from the conta/ct the initial energizlng circuit is broken and-the subsequent opening of the holding circuit by cam lll results in the deenergization of relay lit. The holding circuit is broken by downward movement of interlock lli and the motor 38 is energized to close valve by 'the return of switch lll to its original position.

The energizing circuit for the motor extends through conductors lll and 8f3, switch 'll in engagement with its normally closed contacts, conductor Bil, contact dit, limit 'switch 93 in engagement therewith, conductor 95 to the motor winding and from thence through conductors 96, ill and 88 to the other branch supply conductor ile. Energization of the motor results in closure of valve 32 and the return of the limit switches to the position indicated.

Assuming now that the temperature within the space increases above a predetermined limit, then thermal responsive element engages its associated contact Sil. The result is the energization amarsi of the cooling control relay l2 the first time that cam 46 closes a circuit connecting conductors 58 and 64. The energizing circuit for relay 'l2 is as follows: from the midpoint of the secondary winding of the transformers through conductors 5l and 58, cam follower arm 60 in engagement with its associated contact, conductor 64, thermal vresponsive element 66 in engagement with contact 53, conductor 'l and the relay winding l2 and from thence through conductors i3 and 5B to the terminal of the transformer winding 54. Energization of the relay winding results in upward movement of interlock i8 and switch 'i9 into engagement with their respective normally open contacts. The former energizes a holding circuit for relay l2 through conductors t5 and t3 and cam di' and the latter energizes the cooling control relay litt controlling operation of the compressor motor. rlf'he energizing circuit for relay itt extends from one of the pair of branch supply conductors, through conductor ill, interlock lili in engagement with its associated contacts, conductor ltd, conductor lil, switch l'il in engagement with its normally open contacts, conductors lil@ and lill to the relay winding iilil and from thence through conductor @it to the other of the branch supply conductors tt. Energize.- tion of the relay eects upward movement of its associated armature and the connection of the compressor motor to the source of supply by switches itil. The compressor motor is thereby energized to cool the air passing through the conditioner and it will remain energized until the thermal responsive means moves out of engagement with contact til. The operation of the time controlled means is the same as that described in connection with the heating means because of the fact that the energizing circuit is controlled by cam Il@ and the holding circuit by cam lll. Whenever the temperature decreases below the predetermined upper limit the thermal responsive element moves out of engagement with contact @d and thereafter cam lll will interrupt the holding circuit and deenergize relay l2. The latter in turn deenergizes relay iill through operation of switch T19.

Considering now the operation of the humidifying means it will be seen from the subsequent description that the humidifying means may be operated simultaneously with the heating or cooling means. This operation possesses'the advantageous result that humidification may be had during the performance of either of these functions. While it is uncommon that humidification may be desired during those seasons when cooling is required it may be that it is desirable under certain conditions, as in certain manufacturing processes and the like.

Whenever the humidity responsive element i i2 moves into engagement with contact lili indicating the need for raising the humidity within the space, the humidity control relay i2!! will be energized. The energizing circuit for this relay is as follows: from the midpoint of the secondary winding of the transformer from conductors 5l and 5t, cam follower arm 59 in engagement with its associated contacts, conductor 53, humidity responsive element il? in engagement with contact i it, conductor i2@ and the relay winding |2l and thence through conductor 55 to the other side of the secondary winding 53. Energization of relay mi results in the closure of a holding circuit for the relay and an energizing circuit for solenoid 39, the latter effecting the opening of valve 3l to admit the ow of water to the humidiner. The holding circuit for the relay is as follows: from the midpoint of the secondary winding through conductors l and 58, cam follower arm 52 in engagement with Contact i2?, conductor |26, interlock IIB in engagement with its normally closed contacts, conductor |23, in-

terlock |23 in engagement with its normally open contacts, conductor I 28 leading to the relay winding #2l and from thence through conductor 55 to the tranformer secondary winding section 53. The energizing circuit for the solenoid 39 is as follows: from conductor 87 through the interlock |83 in its closed position, conductors |04 and lli, switch l2@ in engagement with its associated contact, conductor |33 leading to the solenoid winding 39, and from thence through conductors |311, 3l', and 58 to the other of the branch supply conductors 86. Thereupon the humidifying means is rendered effective to humidify the air supplied to space IIJ until such time as the humidity responsive means II2 moves out of engagement with its associated contact. The control of the humidifying means by cams l5 and 48 is exactly the same as that described in connection with the thermal responsive means by cams it and 4'! and will not be described in any greater detail here. Whenever the humidity has been raised sufficiently cam 48 deenergizes the holding circuit for relay I2I and operation of the humidifying means is terminated.

Whenever the humidity in the space I3 increases above predetermined limits humidity responsive element H2 engages contact II3 thereby establishing an energizing circuit for the dehumidifying or cooling control relay H6. The energizingcircuit is as follows: from the midpoint of the secondary winding through conductors 5l and 58, cam follower arm 59 in engagement with its associated contact, conductor 63. humidity responsive element II2 in engagement with contact I I 3, conductor I I5 to the relay winding H5 and thence through conductor 55 to the other terminal of secondary winding section 53. Energization ofthe relay results in the establishment of a holding circuit through conductor |25, interlock H8, conductor |28, and contacts operated by cam 48 and also in the energization of the relay |68 controllingthe energization of the compressor motor. The relay |08 is energized Y through a circuit extending from one of branch supply conductors 86 through conductors 87, interlock |83, conductors |04 and |55, switch H0, conductors |32 and IM leading to the relay winding and from thence through conductor 98 to other branch supply conductor 86. The compressor motor is thereby energized and the refrigerating apparatus again cools the air to condense some of the moisture in the air and thereby decreases its humidity.

Whenever the air within the space has been dehumidied to the desired extent the humidity responsive element moves out of engagement with contact I I3 and thereafter cam will interrupt the holding circuit for relay H6 in a manner that is obvious from the preceding description.

In case the humidity and temperature both exceed predetermined limits, it will be obvious that both the condition responsive means will merely close parallel energizing circuits for the relay |08 by closure of interlocks 'I9 and IIB. This will not result in any harmful effect for as long as the cooling means is operated the temperature will be reduced and, at the same time the humidity will be reduced.

Under some Weather conditions it may be that in order to decrease the humidity to a desired value it may be necessary to reheat the air after it passes by the evaporator 2t. It is obvious that in such event the cooling means will be acting in opposition to the heating means. The former will be effective to decrease the humidity While the latter is eiective to raise the temperature to a desired Value.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. In a system for supplying conditioned medium to a space, the combination including a plurality of condition changing means for conditioning said space, electrical means associated with each of said means for controlling the operation of said means, means including a source of energy, an energizing circuit for each of said electrical means, condition responsive means for selectively closing a portion of said circuit and time controlled means periodically connecting said energizing circuit to said source of energy for selectively initiating operation of said condition changing means and means including said time controlled means and a second circuit periodically energized thereby for maintaining in operation the condition changing means selected for operation by said condition responsive means.

2. In a system for supplying conditioned medium to a space, the combination including a plurality of condition changing means for conditioning said space, electrical means associated with each of said means for controlling the operation of said means, means including a source of energy, an energizing circuit for each of said electrical means, condition responsive means for selectively closing a portion of said circuit and time controlled means for periodically connecting said energizing circuit to said source of energy for selectively initiating operation of said condition changing means, and means including said time controlled means and a second circuit comprising interlocking means operated by said electrical means adapted to be connected to said source of energy by said time controlled means when said lirst circuit is disconnected therefrom for maintaining in operation the condition changing means selected for operation by said condition responsive means.

3. In a control system the combination including a condition responsive means including a member movable in response to changes in said condition and a pair of contact members selectively engaged by said movable member on predetermined movements of the latter from a predetermined normal position, a relay mechanism comprising a pair of relays each connected to a predetermined one of said contact members, asource of energy and electrical connections whereby said relays are energized by said movable member making contact with a corresponding contact, and means for electrically locking each of said relays when energized, said means including interloclrs so connected that one of said relays locks itself in and the other through the interlock controlled by the iirst. i

4. In a control system the combination including a condition responsive means including a member movable in response to changes in said condition and a pair of contact members selectively engaged by said movable member on predetermined movements of the latter from a predetermined normal position, a relay mechanism comprising a pair of relays each connected to a predetermined one of said contact members, a

source of energy and electrical connectionsl whereby said relays are energized by said movable member making contact with a corresponding contact, means for electrically loclring each of said relays when energized, said means including interlocks so connected that one oi7 said relays locks itself in and the other through the interu lock controlled by the rst, and periodically operating means for interrupting alternately said energizing and locking circuits.

5. An electrical relay mechanism comprising a pairof relays, each oi said relays having a Winding and an armature, means including a circuit comprising condition responsive means and a time controlled means iorselectively energizing said windings, and means including a second circuit comprising interlocks operated by said armatures and time controlled means ior electrically locking said relays when energized, the time controlled means being adapted alternately to deenergize their respective circuits.

6. An electrical krelay mechanism comprising a pair of relays, each oi said relays having a winding and an armature, means including a circuit comprising condition responsive'rneans and time controlled means for selectivelyenergizing said windings, and means including a second circuit comprising an interlocking means operated by each of said armatures and time controlled means for electrically locking said relays when energized, said interlocking means being so connected that one oi said relays is locked by the inter-s locking means operated by it and the other jointly by both said interlocking means.

7. In a system ior supplying conditioned medium to a space, the combination including heating means, cooling means, and humidifying means, electrical relays controlling operation oi said heating and humidiiying means, a pair of electrical relays controlling said cooling means, thermal responsive means `Within said space for selectively energizing the relay controlling said heating means and oneoi said pair oi relays controlling said cooling means, and humidity rel sponsive means within said space ror selectively lli energizing the other oi said pair of relays controlling said cooling means and the relay controlling said humidiiying means.,

8. An electrical relay mechanism comprising a relay having a winding and an armature, means including a circuit comprisingcondition respon sive means and a time controlled means periodically rendering said condition responsive means eiective only at recurring short periods for energizing said winding, and means including a second circuit comprising interloclrs operated by said armature and time controlled means for electrically locking said relay when energized at all times other than a portion oi said recurring short periods.

9. ln combination, a relay having an energizing circuit and a holding circuit, and control means therefor including a condition responsive switch in said energizing circuit, a timing device having one switch connected in series `with said condition responsive switch and closing only at recurring short periods, and a second switch connected in said holding circuit and opening only during a portion of each oi' said recurring short periods.

10, Condition response control means including a member movable in response to changes in the condition, a pair of condition controlling contacts opened and closed by said movable member upon predetermined movements of said member, an electrically operated condition control device having an energizing circuit including said pair of conditioning control contacts and an energization maintaining circuit including a pair of maintaining contacts closed upon energization of said device, and a continuously operating timing device having two pairs of synchronized timing contacts, one pair being normally open and closed only periodically for short intervals and connected in series with said pair oi conditioning controlling contacts in said .energizing circuit. and the other pair being normally closed and opened only during a small portion of each of said short intervals and connected in series with said pair of maintaining contacts in said energization maintaining circuit whereby said movable member is rendered effective periodically to cause energization of said condition control device only during said short intervals and to cause deenergization'of said device only during said small portion of said short intervals.

ll. ln combination, in a condition responsive control system, a continuously. operating timer having a pair of synchronized timing circuit controlling means, one for closing a circuit periodically for a relatively short interval and the other for opening a circuit momentarily during said interval, a condition responsive circuit controller having a circuit opening position and a circuit closing position, and electromagnetic control device having a switch operated from the circuit opening to the circuit closing position upon energization of said device, an energization circuit for said device having said one timing circuit controlling means and said condition responsive circuit controller connected in series therein and a holding circuit for said device including said switch and said other timing circuit controlling means connected in series therein.

l2. Condition responsive selective control means including a member movable in response to changes in the condition, selective circuit closing and opening means operatedby said member, a pair of electrically operated condition control devices, each having an energizing circuit selec= tively controlled by said selective circuit closing and opening means and each having an ener gization maintaining circuit including a circuit closing means operated upon the selective energization of the corresponding device, and a continuously operating timing device having a pair of synchronized circuit controlling means, one being normally open and closed only periodically for short intervals and connected in series with said selective circuit closing and opening means to control said energizing circuits and the other beingnormally closed and opened only during a small portion of each or" said short intervals and connected in each of said energization maintaining circuits whereby said movable member is rendered effective periodically to cause selective energization of said condition control devices only during said short intervals and to cause deenerglzation of said devices only during said HARRY R. CRAGO.

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